A new study reveals that plants have their own “ bedtime alarm clock ” that helps them survive the night. Researchers at the University of York have discovered that plants possess an internal signal which they believe tells them     1     amount of sugar they have in their systems at dusk. Plants use sunlight to make     2     ( they ) own sugars from photosynthesis (光合作用）during the day and store them to provide energy during the night.

Plants’ ability to predict sunrise and estimate the     3     ( long ) of the night, as well as adjust metabolism (新陈代谢),     4     ( depend ) on a biological time-keeper called a circadian clock. This is a network of genes which drives rhythms of     5     ( rough ) 24 hours. Biologists think it is this signal, or so-called “ alarm ” ,     6     gives plants the information they need to adjust their metabolism in the dark nighttime hours to stay alive.

The researchers discovered a set of genes     7     ( regulate ) by the chemical compound superoxide, which     8     ( associate ) with metabolic activity. And they found by stopping the production of superoxide, they also stopped the effect of sugar     9     these circadian clock genes in the evening,     10     ( reveal ) the plants’ so-called “ alarm ” .